The invention relates generally to network data storage systems, and relates particularly to enclosures or housings for data storage units which form part of a network data storage system.
With the explosive growth of the Internet and with the growth of client-server systems in both business-to-business and business-to-consumer relationships, there has come to be a profound shift in business and consumer expectations regarding availability and reliability of servers and associated data. Historically many systems were batch-oriented, while nowadays systems are updated in real time. Historically many systems provided information to a small number of people who in turn interfaced with large numbers of people; nowadays customers and users expect to be able to obtain information themselves without having to speak to an intermediary. Historically, in batch-oriented systems, it was a straightforward matter to protect against single-point data loss by simply replicating files before or after the batch processing. In present-day systems where continual updating takes place, no single act of replication provides a complete solution to the problem of backups.
A number of approaches have been devised to deal with such needs. One approach, and historically the first approach, was to attempt to make an arbitrarily reliable disk drive or other storage mechanism. Such an approach is uneconomic, however, and even if cost were of no concern, there are natural upper limits on how reliable a particular storage device can be.
A different approach, called RAID (redundant array of independent disks) has proven to be a much better way to attempt to achieve high reliability in data storage. A RAID system will contain as many as about fourteen disk drives, tied together logically. Versions of RAID have been developed which store each item of data several times on each of several different physical drives. In this way, loss of a single physical drive need not result in loss of any data. Indeed, with appropriate software and system design, it is possible to protect against loss of two drives. Still other versions of RAID permit improved data latency, that is, a reduction in the interval between the time that an item of data is desired and the time that the item of data is retrieved.
Stated differently, RAID permits the use of several relatively inexpensive disk drives of non-perfect reliability, in a system which can be shown to be extremely reliable.
The above-mentioned advantages are found regardless of whether particular physical drives are permanently installed or are removable. But with further advances in hardware and software design, it has become possible for drives to be xe2x80x9chot-swappablexe2x80x9d, meaning that a drive or other system component can be removed while the system is operating, and replaced with a new unit. Under software control, the RAID system can offer seamless service while such swaps are taking place.
Given the many advantages of RAID systems, it is unsurprising that RAID systems have come into commercial use. In recent times the popularity of RAID systems has given rise to a great need for RAID systems of ever-greater capacity and storage density. There are competitive pressures to reduce the cost of RAID systems. Now that the logical function of a RAID system is well defined, attention has shifted to improving the enclosures and other infrastructure for the physical disk drives making up a RAID system.
Most RAID systems are rack-mounted, for example on industry-standard nineteen-inch racks. Each system is thus of a width to fit in the rack, and is of a height to accommodate the height of a disk drive. A plurality of disk drives are mounted in the system, parallel to each other and stacked to reach nearly the width of the rack.
Historical RAID enclosures are typically made of formed sheet metal. Such enclosures don""t always keep their shape well, and some such enclosures can transmit vibration from one disk drive to another, leading to sympathetic vibrations and disk failure. It is important to keep the drives and power supplies from overheating, so cooling is important. Such cooling can be accomplished by a combination of forced-air cooling and other means such as conduction. The bulk material of a sheet-metal enclosure often contributes little to cooling, and in fact may impede cooling.
Formed sheet metal parts give rise to mechanical tolerances which stack up as the parts are assembled. Excessive tolerances can lead to assembled products which are unacceptable to customers for a number of reasons.
It is necessary to provide guideways which permit sliding disk drives into the enclosure. The guideways must satisfy many requirements, for example, they must cause the disk drive""s connectors to align with corresponding connectors on a backplane inside the enclosure. The guideways must also be spaced and shaped to within particular tolerances simply to receive the disk drives. The guideways must provide locking mechanisms to lock disk drives into place, yet must permit a drive to be readily unlocked for removal.
It is also necessary to provide plenums or other air guides so that cooling air from cooling fans can pass over each of the disk drives. It would be unacceptable for any disk drive to be starved of cooling air. Yet a sheet-metal enclosure is relatively expensive to fabricate, especially considering the very demanding requirements for guideways and air plenums. Traditional enclosures are heavy. This adds to shipping costs.
In many enclosures the drive carriers essentially rest on the bottom shelf of the enclosure, leading to biased loading of the bottom shelf wall of the enclosure. Statically, this can lead to a deflection of the bottom shelf wall, causing the enclosure to exceed the permitted envelope for the case, for example to exceed a three-unit rack space by extending downward into the next rack space below. Such deflection also risks loss of the integrity of EMI shielding between the tops of the carriers and the top wall of the enclosure. In an earthquake scenario, deflection could give rise to slapping between adjacent enclosures possibly causing damage to hard drives or modules.
If drive carrier vertical motion is not fully constrained, there is the risk that drive rotational vibration could be coupled back into the enclosure. Such vibration coupling could lead to soft errors. If operating shock or vibration are present, lack of vertical constrain could produce soft drive errors or could even lead to intermittent or consistent disconnects at the electrical connector that joins the drive and the mother board.
Some prior art designs have employed large deflection spring fingers to attempt to vertically constrain the carriers in the enclosure, but this is not wholly satisfactory.
There is thus a great need for an enclosure for a disk storage system that keeps its shape well, that provides guideways for disk drives, that allows for easy provision of air plenums, that helps rather than hinders cooling, that doesn""t weigh as much, and that can be economically manufactured.
A shelf enclosure for a network data storage system employs drive carriers having wedge mechanical interfaces with respective features on the enclosure, locking into place at the top and bottom of the carriers.